ACTIVE AUDIO NOISE CANCELLING

• US 20110249826A1
• Filed: 12/11/2009
• Published: 10/13/2011
• Est. Priority Date: 12/18/2008
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Van Leest, Adriaan Johan
• Granted Patent: US 8,948,410 B2
• Time in Patent Office: Days
• US Class Current: 381/71.8
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17861 using additional means for damping sound, e.g. using sound absorbing panels
• CPC Class Codes: G10K 11/17875 using an error signal without a reference signal, e.g. pure feedback
• CPC Class Codes: G10K 11/17885 additionally using a desired external signal, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 2210/3026 Feedback
• CPC Class Codes: G10K 2210/3056 Variable gain

Abstract

A noise canceling system comprises a microphone (103) generating a captured signal and a sound transducer (101) radiating a sound canceling audio signal in the audio environment. A feedback path (109) from the microphone (103) to the sound transducer (101) comprises a non-adaptive canceling filter (115) and a variable gain (117) and receives the captured signal and generates a drive signal for the sound transducer (101). A gain detector determines a secondary path gain for at least part of a secondary path of a feedback loop. The secondary path may include the microphone (103), the sound transducer (101), and the acoustic path therebetween but does not include the non-adaptive canceling filter (115) or the variable gain (117). A gain controller (121) adjusts the gain of the variable gain (117) in response to the secondary path gain. The system uses simple gain estimation and control to efficiently compensate for variations in the secondary path to provide improved stability and noise canceling performance.

Claims

1. A noise canceling system comprising:

a microphone (103) for generating a captured signal representing sound in an audio environment;

a sound transducer (101) for radiating a sound canceling audio signal in the audio environment;

a feedback means (109) from the microphone (103) to the sound transducer (101), the feedback means (109) receiving the captured signal and generating a drive signal for the sound transducer (101) and comprising a non-adaptive canceling filter (115) and a variable gain (117);

gain determining means (119) for determining a secondary path gain for at least part of a secondary path of a feedback loop, the feedback loop comprising the microphone (103), the sound transducer (101) and the feedback means (109) with the secondary path not including the non-adaptive canceling filter (115) and the variable gain (117); and

gain setting means (121) for adjusting a gain of the variable gain (117) in response to the secondary path gain.

2. The noise canceling system of claim 1 wherein the gain determining means (119) comprises:

means (701, 703) for injecting a test signal in the feedback loop;

means for determining a first signal level corresponding to the test signal at an input of the at least part of the secondary path;

means for determining a second signal level corresponding to the test signal at an output of the at least part of the secondary path; and

means for determining the secondary path gain in response to the first signal level and the second signal level.

3. The noise canceling system of claim 2 wherein the output of the at least part of the secondary path corresponds to at least one of an input of the variable gain 117 and an input of the non-adaptive canceling filter (115).

4. The noise canceling system of claim 2 wherein the means for determining the first signal level is arranged to determine the first signal level in response to a signal level of the test signal and without measuring a signal of the feedback loop.

5. The noise canceling system of claim 2 wherein the test signal is a narrowband signal having a 3 dB bandwidth of less than 10 Hz.

6. The noise canceling system of claim 2 wherein the test signal is substantially a sinusoid.

7. The noise canceling system of claim 2 wherein the test signal has a central frequency within an interval from 10 Hz to 40 Hz.

8. The noise canceling system of claim 2 wherein the test signal is a noise signal.

9. The noise canceling system of claim 2 further comprising:

means for measuring a third signal level for a signal corresponding to the input of the at least part of the secondary path in the absence of the test signal; and

means for setting a signal level of the test signal in response to the third signal level.

10. The noise canceling system of claim 2 wherein an attenuation of a signal component corresponding to the test signal by the non-adaptive canceling filter is at least 6 dB.

11. The noise canceling system of claim 1 further comprising means for feeding a user audio signal to the sound transducer (101), and wherein the gain determining means (119) comprises:

means for determining a first signal level corresponding to the user audio signal at an input of the at least part of the secondary path;

means for determining a second signal level corresponding to the user audio signal at an output of the at least part of the secondary path; and

means for determining the secondary path gain in response to the first signal level and the second signal level.

12. The noise canceling system of claim 1 wherein the gain setting means is arranged to set the gain of the variable gain such that a combined gain of the secondary path gain and the gain of the variable gain has a predetermined value.

13. The noise canceling system of claim 1 wherein the at least part of the secondary path comprises an acoustic path from the sound transducer (101) to the microphone (103).

14. The noise canceling system of claim 1 wherein the secondary path comprises a digital section and the at least part of the secondary path comprises at least one of an analog to digital converter (107) and a digital to analog converter (111).

15. A method of operation for a noise canceling system including:

a microphone (103) for generating a captured signal representing sound in an audio environment;

a sound transducer (101) for radiating a sound canceling audio signal in the audio environment;

a feedback means (109) from the microphone (103) to the sound transducer (101), the feedback means (109) receiving the captured signal and generating a drive signal for the sound transducer (101) and comprising a non-adaptive canceling filter (115) and a variable gain (117);

the method comprising;

determining a secondary path gain for at least part of a secondary path of a feedback loop, the feedback loop comprising the microphone (103), the sound transducer (101) and the feedback means (109) with the secondary path not including the non-adaptive canceling filter (115) and the variable gain (117); and

adjusting a gain of the variable gain (117) in response to the secondary path gain.